Switching mechanism



NOV. 8, 1955 J, HARRIS 2,723,320

SWITCHING MECHANISM Filed March 22, 1952 Unite States 2,723,320 PatentedNov. 8, 1955 The present invention relates in general to switchingmechanism and more particularly to switches adapted for operation bytiming mechanisms.

The primary object of the invention is to provide a simple and positiveswitch which opens and closes with snap action even though operated by adevice having an extremely slow motion.

A further object of the invention is to provide a switching mechanismhaving an operator normally biased in one direction but in which thebiasing action may be discontinued at will to provide manual control.

Other objects will appear from the following description and appendedclaims.

For a full disclosure of the invention reference is made to thefollowing detailed description and to the accompanying drawing in which:Figure l is a front view of a timing mechanism incorporating one form ofswitch embodying the invention and with parts broken away to show theswitch construction. Figure 2 is a side view of the mechanism shown inFigure 1. Figure 3 is a sectional view taken on line III1II of Figure 1.Figure 4 is a view similar to Figure 1 showing the switch mechanismapplied to a different form of timer.

Referring to Figures 1 and 2, reference character 1 indicates a frontpanel which supports a plate 2 by means of spacers 3. The plate 2carries a synchronous timing motor generally indicated as 4. This motordrives a gear reduction unit 5, which in turn rotates a shaft 6 which ismounted between plates 1 and 2. The shaft 6 carries a hub 7 whichsupports a dial 8, an on cam 9, and an 01f cam 10. The on and off cams 9and 10 operate a cam follower 11 which is carried by a cam shaft 12which is supported between plates 1 and 2. The cam follower consists ofan L-shaped member and is secured to the shaft along with a pointer 13by means of a screw 14. The cam shaft 12 supports a cam 15 betweenplates 1 and 2. Preferably the portion of the cam shaft between plates 1and 2 is hexagonal in shape as shown in Figure 2 for preventing relativerotation between the cam shaft and cam.

Mounted on the plate 2 is a switch panel 16 which supports a switchblade bracket 17 and a contact bracket 18. The bracket 17 supports aswitch blade 19 carrying a contact 20 which cooperates with a similarcontact carried by the bracket 18. As shown in Figure 1, the switchblade is provided with an offset portion 21 which is engaged by lobe 22of the cam 15. Lobe 23 of the cam engages a cam follower 25 which issupported on a stud 26 mounted on plate 2. This cam follower in turnoperates a latch 27, which is supported on a stud 28 which in turn ismounted on plate 2. As shown more clearly in Figure 3, the latch 25 isbiased toward the cam by means of a torsion spring 30. One end of thisspring rides on the stud 28 and the other end bears against an inturnedportion 31 of the cam follower. The latch 27 is provided with a biasingspring 32 which biases the latch toward the switch blade.

The invention is shown applied to a defroster control for refrigerators,the function of which is to prevent operation of the refrigerator forseveral hours each night. Thus the off cam 10 is provided with a notch35 into which the cam follower drops at a point indicated at 12:30 onthe dial 8. The on cam 9 has a finger 36 which raises the cam follower11 off the periphery of cam 10 at a point indicated at approximately4:30 on the dial 8.

The dial and cams are driven in a clock-wise direction at a speed of onerevolution a. day. With the parts in the position shown, the camfollower 11 has just dropped in the notch 35 and again returned to theperiphery of cam 10. This action has opened the switch permitting thelatch member 27 to come under blade 19 thus preventing contact 20 fromengaging its cooperating stationary contact. The lobe 22 of the cam forthis position of the cam follower is approximately at the top of theoffset portion 21. This has applied pressure to the switch blade 19sufliciently to cause the contacts to engage. However, due to the latchmember 27, the contacts are restrained from engagement.

As the dial rotates, the projection 36 of the on cam comes under the camfollower 11, causing counter-clockwise rotation of the cam 15. Thisrotates the cam follower 25 in a clockwise direction which in turnrotates the latch 27 in a counter-clockwise direction. When the camfollower 11 is approximately half-way up the projection 36, the latch 27disengages the end of a switch blade 19. The switch blade, due to itsresiliency, snaps downwardly for causing the contacts to engage. Uponcontinued motion of the dial assembly, the projection 36 rides out fromunder cam follower 11 which permits this cam follower to be returned tothe periphery of cam 10 by means of the cam follower spring 26. The cam15 returns to the position shown in Figure 1. However the contactsremain closed due to the latch 27 being out from under the end of switchblade 19. The parts remain in this position until the notch 35 and offcam 10 comes under cam follower 11. The cam follower drops into thisnotch with snap action thus permitting clockwise rotation of the cam 15.The lobe 22 of this cam moves to the left, thus permitting blade 19 tomove upwardly under its bias. This causes the contacts to open andpermits the latch 27 to be returned to its position under the switchblade by means of spring 28. As the dial assembly continues to rotate,the cam follower 11 rides up the inclined portion of the notch 35 whichin turn causes the lobe 22 of the cam to ride up the inclined portion 21of the switch blade. This returns the parts to the position shown inwhich the contact closing force has been applied to the switch blade andin which the contacts are prevented from closing by means of the latch27.

In a defroster control it is desirable occasionally to preventdefrosting on certain nights such as when icecream is being stored inthe freezing compartment. When the user wishes to skip a defrost cycle,the pointer 13 is moved to the right as far as permitted by the stop pin37 which limits the motion of the cam 15. During this movement of thecam 15 the end of the cam follower 25 rides from the side of the lobe 23to the top thereof. This neutralizes the biasing action of the camfollower 25 on the cam which permits the parts to remain in thisposition in which the contacts 20 are closed. When the user wishes toreturn to automatic defrost operation, the pointer 13 is moved back tothe position shown, in which the biasing action of the cam followerspring 26 maintains the cam follower in an engagement with the on" andoff cams 9 and 10.

Referring to Figure 4 the switch is operated by means of on and offpointers 51 and 52 which are provided with inwardly extending tongues 53and 54 respectively. These tongues engage out-turned portions 55 and 56of a 9 a pointer 57 which is mounted on the shaft 12. Thus, as the onpointer 52 rotates past the pointer 57, the lug54 engages the lug 55 ofthe pointer, causing counter-clockwise rotation of the cam 15. Thisrotation of the cam first drives the switch blade downwardly and thenreleases the latch 27 which permits the contacts to close with snapaction. The parts are proportioned so that the lobe 22 of the cam ridesbeyond the top of the offset portion 21 of the switch blade. Thus thebiasing action of the switch blade on the cam becomes neutralized, andthe cam remains in the on position. As the off pointer 51 passes thepointer 57, the tongue 53 thereof engages the projection 56 causingclockwise rotation of the cam shaft. When the lobe 22 rides out to theoffset portion 2t of the switch blade, a component of force appears,which causes rotation of the cam by the biasing action: of the switchblade. This causes snap action rotation of the cam which permits snapaction upward movement of the switch blade for disengaging the contacts.

It will be observed that the switching mechanism of Figure 4 isidentical in construction with that shown in Figure l with the exceptionthat the cam follower spring 26' is formed so as to reduce the travel ofthe cam follower caused by this spring. This eliminates the springreturn action by the cam follower so that the parts may remain in the onposition.

From the foregoing it will be apparent that the present inventionprovides a simple and positive snap action switching mechanism which maybe used in a variety of applications. While a preferred form of theinvention has been disclosed it will be apparent that many modificationsmay be made without departing from the spirit and scope of theinvention. It is desired, therefore, to be limited only by the scope ofthe appended claims.

I claim:

1. In a switch construction, the combination of, a switch blade anchoredat one end and carrying a first contact, a second contact cooperatingwith said first contact, an operator arranged to engage the blade on theside there of opposite the contacts for forcing the same intoengagement, the switch blade being biased toward said operator, a latcharranged to engage the blade at a point substantially spaced from saidoperator and prevent engagement of said contacts by said operator, andmeans operated with said operator for releasing said latch when theoperator reaches a pre-determined position when moving in contactengaging direction.

2. In a switch construction, the combination of a switch blade anchoredat one end and carrying a first contact, a second contact cooperatingwith said first contact, said switch blade having an offset portion, arotatable cam having a segment constructed and arranged to engage andride up the offset portion for applying pressure to the blade in contactengaging direction, a latch arranged to engage the blade at a pointsubstantially spaced from the offset portion and prevent engagement ofthe contacts, and means operated by said cam for releasing said latch.

3. In a switch construction, the combination of a switch blade anchoredat one end and carrying a first contact, a second contact cooperatingwith said first contact, an operator arranged to engage the blade on theside thereof opposite the contacts for forcing the same into engagement,the switch blade being biased toward said operator, a latch arranged toengage the blade at a point substantially spaced from said operator andprevent engagement of said contacts by said operator, and a cam followerarranged to ride the cam at a point spaced from the switch blade, saidcam follower also being arranged to engage and operate the latch forreleasing the same at a predetermined position of said cam.

4. In a switch construction, the combination of a switch blade anchoredat one end and carrying a first contact, a second contact cooperatingwith said first contact, an operator arranged to engage the blade on theside thereof opposite the contacts for forcing the same into engagement,the switch blade being biased toward said operator, a latch arranged toengage the blade at a point substantially spaced from said operator andprevent engagement of said contacts by said operator, and a cam followerarranged to ride the cam at a point spaced from the switch blade, saidcam follower also being arranged to engage and operate the latch forreleasing the same at a predetermined position of said cam, said camfollower being provided with a spring for biasing the cam in contactopening direction, said cam and cam follower being proportioned so as toneutralize the biasing offset of the cam follower on the cam when thecam is rotated beyond a pro-determined angular position.

References Cited in the file of this patent UNITED STATES PATENTS1,510,901 Nowosielski Oct. 7, 1924

